How to check duplicate string array in list?

December 20, 2022

How to check duplicate string array in list?
I declare string array list like this:

List<string[]> list = new List<string[]>();

and I add a few items in the list.

list.Add(new string[3] {"1","2","3"});
list.Add(new string[3] {"2","3","4"});
list.Add(new string[1] {"3"});
list.Add(new string[1] {"3"});
list.Add(new string[3] {"1","2","3"});

now I want to get to know which items are duplicated. I tried like below to add the duplicated items to new list:

for (int j = 0; j < list.Count - 1; j++)
{
    for (int k = list.Count - 1; k > j; k--)
    {
        if (j != k)
        {
            if (Enumerable.SequenceEqual(list[j], list[k]))
            {
                savedDistinctList.Add(list[j]);
            }
        }
    }
}

and finally I want to remove the duplicated item in the first list. so I want to see 3 items in the list.([1,2,3],[2,3,4],[3])

Perhaps any idea using LINQ or something else?

>Solution :

First we have to teach .Net how to compare arrays:

private sealed class ArrayEqualityComparer<T> : IEqualityComparer<T[]> {
  public bool Equals(T[] left, T[] right) {
    if (ReferenceEquals(left, right))
      return true;
    if (left is null || right is null)
      return false;

    return left.SequenceEqual(right);
  }

  public int GetHashCode(T[] array) => array is null
    ? -1
    : array.Length;
}

Then you can use Linq Distinct with this class implemented:

using System.Linq;

...

savedDistinctList = list
  .Distinct(new ArrayEqualityComparer<string>())
  .ToList();

If you want to modify the existing list, you can use HashSet<T>:

var unique = new HashSet<string[]>(new ArrayEqualityComparer<string>());

for (int i = list.Count - 1; i >= 0; --i)
  if (!unique.Add(list[i]))
    list.RemoveAt(i);